Question: Compression on a marine diesel engine?

(Posted by: on 2010-08-02 17:31:15)

I have a yanmar ysb8 engine, it has low compression, what has to be done to that engine to make it right? It was checked out my a yanmar mech. but I was not there and he didn't tell me how he came to that conclusion' there is a little black smoke when I first start it, and also if I give it to much throttle, yes it has a compression release it is in the right position, I believe it is the orig. engine 1978, it tries to start and almost does, but I am not sure how many times I should kept tring, after a half dozens tries I spray amilla second of starting and it starts. I bought a new fuel injector but the mechanics I have had down to the boat said it wouldn't make any difference

Posted by: 45 auto on 2010-08-02, 17:57:03

First did U do a dry test than a wet test. To see if it's valves or rings. I had a 3 cylinder Westerbeke . and had low power rebuilt the complete engine and head injection pump and injector. Started it up and still had no power. It turned out to be the exhaust elbow it was plugged except for a 3/ 8 hole cleaned it out and it ran great. Yanmar have a large problem with exhaust elbows which can cause low compression and low power. Make sure it free and clear before going threw the rebuild issues

Posted by: Brian on 2010-08-03, 00:31:47

What are the symptons that leed you to this conclusion. Compression is relative, check all cylinders and if there is more than 10% variance then you have identified a problem, Cylinder head gasket is a regular cause of loss at individual cylinders, Valve clearences, tappets clearences are easily checked. Last thing is timeing marks before major is stripdown. Always look for the simple solutions first,